Tire blowouts or tread separation has been in the news a lot because of a Firestone defective tire recall. Tread separation, however, is not a new problem. Most tires manufactured today are steel belted radial tires, and tread separation is the most common type of failure in steel belted radial tires. When the tread separates from the carcass or the inner plies, it can frequently cause a blowout. Tire blowouts can also cause the driver to lose control of the vehicle, resulting in collisions and rollovers. Loss of control is especially likely in vehicles with a high center of gravity, such as many popular sport utility vehicles.
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Tires are built in layers on a machine. The tire is built in the green or uncured state, and the core or carcass of the tire is sometimes referred to as the “green tire”.
During the manufacture of a steel belted radial tire, a layer of skim stock is applied to the green tire and then the steel belts are applied around the green tire. Another layer of skim stock is then applied and then the tread is applied around the belts. The entire tire is then subjected to high temperatures and pressures to cure the tire assembly. After it has been cured, the tire is mounted on a rim and permitted to cool.
Tire tread belt separations are an inherent by-product of steel belted radial tires and can be caused by both design and manufacturing defects. While steel belted radial tires have the advantage of providing impact and puncture resistance, the use of steel belts is inherently problematic because rubber will not adhere to steel. To obtain adhesion of the rubber tread to the steel belts, tire makers coat the steel with brass. Rubber will adhere to brass, but brass has a tendency to break down quickly.
In many tread separation incidents, the failure is at the first level of skim compound where the tread just peels off. In other incidents, the failure occurs at the level of the green tire. While failure at the level of the green tire may sometimes be referred to as a tire carcass failure, it can also be referred to as a tread separation.
Contact a defective tire lawyer at Jim S. Adler & Associates if you or a loved one were involved in a car accident caused by a defective tire. The firm offers a free case review.
In any case involving defective tire tread separation, efforts should be made to inspect and photograph the tire and tread immediately. In a properly designed and manufactured tire, you should typically not see a bare wire surface. The presence of bare wire after a tread separation indicates that the tire was not properly cured and can indicate a manufacturing adhesion defect. The presence of brassy wire is also indicative of a defect since brassy wire indicates there was essentially no curing and no adhesion of the belt to the surrounding rubber. Corroded wire might reflect moisture contamination during manufacturing. Because the defense will likely argue that any corrosion occurred naturally during the post-accident period, early photographs are particularly important in addressing corrosion issues.
As mentioned, tread separation can occur as a result of both design and manufacturing defects. Tread separations can frequently be traced to poor bonding or adhesion of the tire components during manufacturing.
Tire plants frequently emphasize quantity over quality, which leads to lax quality control practices. Poor quality control and manufacturing practices can result in moisture, foreign matter and other impurities getting cured into the tire. The moisture and impurities can lead to a tread separation when the tire is put into use. Because tires are made by hand, perspiration and dirt from the workers’ hands can contaminate the defective tire and cause tread separation. Inadequate or over aged skim stock can also lead to tread separation. Manufacturers sometimes use solvent between the belts to restore skim stock that should be thrown out. The use of certain solvents on tire components and between the belts can lead to tread separation. During the final inspection stage of tire production, defects that should otherwise be spotted are sometimes allowed to slip through the inspection. Final inspections that should take about 2 minutes per tire take as little as 15 seconds in some plants.
Design defects that contribute to tread separation include deficient skim stock and the lack of nylon overlays. Improving the skim stock can lead to better adhesion or bonding of the rubber to the steel and thus make tread separation less likely. A nylon overlay, which consists of a nylon “safety belt” between the tread and the steel belts, can also make tread separations less likely. The nylon overlay placed over the steel belts acts like a “tourniquet” by providing stability to the interior components of the tire. It also assists in resisting moisture intrusion into the tire. Nylon also contracts when heated and acts to pull the components of the tire together when the tire starts to heat up.
Unfortunately, U.S. tire manufacturers have resisted the use of nylon overlays. Although it has been estimated that nylon overlays will only increase the cost of a tire by about a dollar, nylon overlays have typically been used only in “high performance” tire lines.
Defective tires will sometimes separate wholly or partially off of their rim, at the level of the tire beads, resulting in an immediate loss of tire pressure. This phenomenon is known as “debeading” and can contribute vehicle rollover. An under inflated tire or a tire with a specified air pressure that is too low might be more likely to debead during severe turns.
During rollover testing conducted by the National Highway Traffic Safety Administration in 1998, two Ford vehicles equipped with Firestone tires that have now been recalled experienced debeading of their front tires. In the NHTSA report, test drivers were noted to be so concerned about the potential debeading that they did not drive the Ford vehicles to the maximum test speeds in later testing.
It should be noted that tires frequently become debeaded during a rollover. The presence of a debeaded tire therefore does not mean the debeading had anything to do with causing the rollover. A careful forensic inspection of the tire and the road, however, can help determine the point or timing of the debead. A rim scrape on the road surface, for example, is consistent with debeading occurring at or prior to the point of rollover.
A tire speed rating reflects the outer speed limits at which the tire can be safety driven. It is now common industry practice to equip vehicles with tires that are speed rated at something greater than the maximum speed capability of the particular vehicle. It is advisable not to exceed a speed rating, which many companies describe as the upper limit for that tire. Speed ratings also assume a certain range of ambient temperature, and a given speed rating could be too high in excessively hot temperatures. Increasing tire loads can also increase the possibility that the defective tire will fail before reaching its speed rating.
If there is only a small margin of safety in the speed rating, a tire might fail due to a combination of speed, heavy load and high ambient temperature. If a tire appears to have failed when a speed rating was exceeded, the tire itself might have been inadequate for the particular vehicle.
Sometimes the problem is not a defect in the tire itself but simply the wrong type of tire for the vehicle at issue. Manufacturers of certain sport utility vehicles have increased tire sizes to improve the tough and rugged image of those vehicles. The Chrysler Jeep Cherokee, for example has been demonstrated by test drivers to be relatively stable when equipped with the tires that came on the vehicle in the 1980s. The Cherokee, however, has been shown to roll over on smooth dry road when equipped with the slightly larger tires that became standard equipment during the 1990s. Larger tires raise the height of the center of gravity of sport utility vehicles and lower the frictional side forces (exerted by the tires sliding on the road) necessary to tip the vehicle over. Larger and wider tires can also result in more tire surface in contact with the road, thereby increasing the frictional forces caused in a sideways slide.
Some tire defects can cause catastrophic failure during the mounting or inflation of tires. When death or serious injuries occur during the tire mounting or inflation process, several possible defects should be investigated.
Multi-piece wheels or rim explosions have caused serious injury and death to tire mounters. Multi-piece rims come in various potentially dangerous configurations. The best practice is to replace multi-piece rims with a single piece configuration that eliminates the potential hazard.
Zipper failures can occur during the tire inflation process. When this occurs, the sidewall of the tire can burst and cause injuries. The rupture patterns of the sidewall often resemble a zipper.
Tire bead failure may occur during the tire inflation process at relatively low air pressures. Bead failures can result in an explosion that causes serious injury or death. Consult a defective tire attorney about your options in such a case.